Dunno, I'm not much of a speaker expert. All I know is I tried putting the bird's old premium speakers into the Cougar's non-premium system, got very weak and crappy sounding audio, put the old speakers back in and I still had the weak and crappy sounding audio. New head unit and all is well.

I really don't know what happened, I just speak from experience. In my case, a stock 94 non-premium head unit with the premium speakers out of the 97. I was installing them trying to get a better sound. I did the driver's side then decided to test them. Initially it sounded like no sound was coming out of them (sound was coming out of the pass. speakers), then I turned the balance all the way left. They were making sound but they were very quiet and the sound was terrible (nothing under say, 500 Hz). I put the stockers back in and expected things to be the way they were before, but the stock speakers were really quiet and again, sounded terrible. I had to have the balance at about 85% left to achieve a balanced sound until I replaced the head unit.

I really don't know what happened, I just speak from experience. In my case, a stock 94 non-premium head unit with the premium speakers out of the 97. I was installing them trying to get a better sound. I did the driver's side then decided to test them. Initially it sounded like no sound was coming out of them (sound was coming out of the pass. speakers), then I turned the balance all the way left. They were making sound but they were very quiet and the sound was terrible (nothing under say, 500 Hz). I put the stockers back in and expected things to be the way they were before, but the stock speakers were really quiet and again, sounded terrible. I had to have the balance at about 85% left to achieve a balanced sound until I replaced the head unit.

OK. You talking about the 5x7 Ford PSS speakers? Or the two way JBL PSS speakers? (There ARE two different designs, you know.) the JBLs are mid/tweeter only, no low end to them at all.

I will say that if they blew your head unit, it was already screwed - they're STILL about 8 ohms IIRC (could pull one and look, but am too lazy to check one of my spares.) Same impedance as the 5x7s, BTW ...